From a female perspective, pregnancy is always a huge investment. Even more so if her species has a hemochorial placenta. Once that placenta is in place, she not only loses full control of her own hormones, she also risks hemorrhage when it comes out. So it makes sense that females want to screen embryos very, very carefully. Going through pregnancy with a weak, inviable or even sub-par fetus isn't worth it.
That's where the endometrium comes in. You've probably read about how the endometriu...

You will be thinking that we are coming to the end of this book: we’ve dealt with eight centuries, so there are only two to go. You may be surprised to learn, therefore, that in historical terms we are not even halfway. The reason for this discrepancy is that history is not time, and time is not history. History is not the study of the past per se; it is about people in the past. Time, separated from humanity, is purely a matter for scientists and star-gazers. If a previously unknown uninha...

As the epochs passed, the two species molded one another to form a well-integrated union. The little arachnoid, no bigger than a chimpanzee, rode in a snug hollow behind the great "fish's" skull, his back being stream-lined with the contours of the larger creature. The tentacles of the ichthyoid were specialized for large-scale manipulation, those of the arachnoid for minute work. A biochemical interdependence also evolved. Through a membrane in the ichthyoid's pouch an exchange of endocrine ...

Scent seems to have all the disadvantages and none of the advantages, as a long-range sense. However, under special circumstances even a modified nose may fill the need. In a story of my own some years ago ("Uncommon Sense," Astounding Science Fiction, September 1945), I assumed an airless planet, so that molecules could diffuse in nearly straight lines. The local sense organs were basically pinhole cameras, with the retinal mosaic formed of olfactory cells. Since the beings in question were ...

Now we get to the core of the simulation argument. This does not purport to demonstrate that you are in a simulation. Instead, it shows that we should accept as true at least one of the following three propositions:
(1) The chances that a species at our current level of development can avoid going extinct before becoming technologically mature is negligibly small
(2) Almost no technologically mature civilisations are interested in running computer simulations of minds like ours
(3) You are...

1. First, you start with soil. We identify what nutrition the soil lacks.
2. Then we identify what species we should be growing in this soil, depending on climate.
3. We then identify locally abundant biomass available in that region to give the soil whatever nourishment it needs. This is typically an agricultural or industrial byproduct — like chicken manure or press mud, a byproduct of sugar production — but it can be almost anything. We’ve made a rule that it must come from...

Imagine a spaceship full of sleeping explorers, deep-frozen would-be
colonists of some distant world. Perhaps the ship is on a forlorn mission to save the species before an unstoppable comet, like the one that killed
the dinosaurs, hits the home planet. The voyagers go into the deep-freeze
soberly reckoning the odds against their spaceship's ever chancing upon
a planet friendly to life. If one in a million planets is suitable at best, and
it takes centuries to travel from each star to the nex...

The designers of our species set out to produce a being that might be capable of an order of mentality higher than their own. The only possibility of doing so lay in planning a great increase in brain organisation. But they knew that the brain of an individual human being could not safely be allowed to exceed a certain weight. They therefore sought to produce the new order of mentality in a system of distinct and specialised brains held in "telepathic" unity by means of ethereal radiation. Ma...

"The project was cancelled," said Nessus. "We found that the Man-Kzin wars put sufficient restriction on kzinti expansion, made you less dangerous. We continued to watch.
"Six times over several centuries, you attacked the worlds of men. Six times you were defeated, having lost approximately two-thirds of your male population in each war. Need I comment on the level of intelligence displayed? No? In any case, you were never in real danger of extermination. Your nonsentient females were lar...

In proportion as physical characteristics become of less importance, mental and moral qualities will have an increasing importance to the well-being of the race. Capacity for acting in concert, for protection of food and shelter; sympathy, which leads all in turn to assist each other; the sense of right, which checks depredation upon our fellows ... all qualities that from earliest appearance must have been for the benefit of each community, and would therefore have become objects of natural ...